Amino derivatives of glycyrrhetinic acid as potential inhibitors of cholinesterases

Article abstract of DOI:10.1016/j.bmc.2014.04.046

The development of remedies against the Alzheimer's disease (AD) is one of the biggest challenges in medicinal chemistry nowadays. Although not completely understood, there are several strategies fighting this disease or at least bringing some relief. Dur

Full text of DOI:10.1016/j.bmc.2014.04.046

Accepted Manuscript
Amino derivatives of glycyrrhetinic acid as potential inhibitors of cholinestera-
ses
Stefan Schwarz, Susana Dias Lucas, Sven Sommerwerk, René Csuk
PII:
S0968-0896(14)00311-3
DOI:
http://dx.doi.org/10.1016/j.bmc.2014.04.046
BMC 11541
Reference:
Bioorganic & Medicinal Chemistry
To appear in:
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Revised Date:
Accepted Date:
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15 April 2014
24 April 2014
Please cite this article as: Schwarz, S., Lucas, S.D., Sommerwerk, S., Csuk, R., Amino derivatives of glycyrrhetinic
acid as potential inhibitors of cholinesterases, Bioorganic & Medicinal Chemistry (2014), doi: http://dx.doi.org/
10.1016/j.bmc.2014.04.046
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Graphical abstract:
Amino derivatives of glycyrrhetinic acid as potential inhibitors of cholinesterases
Stefan Schwarz1, Susana Dias Lucas2, Sven Sommerwerk1, and René Csuk*1
1 Bereich Organische Chemie, Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Str. 2, D-06120 Halle (Saale),
Germany;
2 Instituto de Investigação do Medicamento (iMed.ULisboa), Faculdade de Farmácia, Universidade de Lisboa, Av. Prof.
Gama Pinto,1649-003 Lisboa, Portugal;
Graphical abstract
Amino derivatives of glycyrrhetinic acid as potential inhibitors of cholinesterases
Stefan Schwarz1, Susana Dias Lucas2, Sven Sommerwerk1, and René Csuk*1
1 Bereich Organische Chemie, Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Str. 2, D-06120 Halle (Saale),
Germany;
2 Instituto de Investigação do Medicamento (iMed.ULisboa), Faculdade de Farmácia, Universidade de Lisboa, Av. Prof.
Gama Pinto,1649-003 Lisboa, Portugal;
Corresponding author:
Prof. Dr. René Csuk
Martin-Luther-Universität Halle-Wittenberg
Institut für Chemie – Organische Chemie
Kurt-Mothes-Str. 2
D-06120 Halle (Saale)
Germany
Tel.: +49 345 5525660
Fax: +49 345 5527030
e-mail: rene.csuk@chemie.uni-halle.de
1

Abstract:
The development of remedies against the Alzheimer’s disease (AD) is one of the biggest challenges in medicinal
chemistry nowadays. Although not completely understood, there are several strategies fighting this disease or at least
bringing some relief. During the progress of AD, the level of acetylcholine (ACh) decreases; hence, a therapy using
inhibitors should be of some benefit to the patients. Drugs presently used for the treatment of AD inhibit the two ACh
controlling enzymes, acetylcholinesterase as well as butyrylcholinesterase; hence, the design of selective inhibitors is
called for. Glycyrrhetinic acid seems to be an interesting starting point for the development of selective inhibitors.
Although its glycon, glycyrrhizinic acid is known for being an AChE activator, several derivatives, altered in position
C-3 and C-30, exhibited remarkable inhibition constants in micro-molar range. Furthermore, five representative
compounds were subjected to three more enzyme assays (on carbonic anhydrase II, papain and the lipase from Candida
antarctica) to gain information about the selectivity of the compounds in comparison to other enzymes. In addition,
photometric sulforhodamine B assays using murine embryonic fibroblasts (NiH 3T3) were performed to study the
cytotoxicity of these compounds. Two derivatives, bearing either a 1,3-diaminopropyl or a 1H-benzotriazolyl residue,
showed a BChE selective inhibition in the single-digit micro-molar range without being cytotoxic up to 30 µM. In silico
molecular docking studies on the active sites of AChE and BChE were performed to gain a molecular insight into the
mode of action of these compounds and to explain the pronounced selectivity for BChE.
Keywords: Glycyrrhetinic acid, Ellman’s test, cholinesterase inhibitors, docking studies
1. Introduction
Leading a healthy life is the aim for most of the people living in the western hemisphere. However, a long lifespan as
well as modern living standards go along with an increase of so-called “lifestyle diseases”, e.g. cancer or cardiovascular
problems. Neurodegenerative diseases, especially dementia gain more and more of importance in ageing societies.
Especially the number of patients suffering from Alzheimer’s disease (AD) increased continuously during the last
decades. Meanwhile AD is regarded the most common illness of over-60-year old people1.
One characteristic feature of AD is a decreased level of the neurotransmitter acetylcholine (ACh). This results in a
decline in memory and recognition2-4. Usually, the level of ACh is controlled by the enzyme acetylcholinesterase
(AChE, E.C. 3.1.1.7), which cleaves the transmitter in the postsynaptic area. Another enzyme, butyrylcholinesterase
(BChE, E.C. 3.1.1.8) is also able to hydrolyze ACh, albeit it doesn’t possess the same affinity for the transmitter as
AChE5 does. Less attention has been paid to this fact for a long time, since AChE and not BChE is the predominant
ACh cleaving enzyme in the human brain6. Thus, drugs already introduced into an emerging market for the treatment of
AD are non-selective (rivastigmine7) or AChE-selective inhibitors (galantamine8 or donepezil9, 10). However, those
drugs retard the progress of AD only in a very early stage; during the progress of AD, the loss of AChE-activity is
compensated by BChE11, 12. Thus, the BChE/AChE-ratio changes from 0.2 in normal human brains to approximately 11
in AD brains13. Furthermore, a correlation between BChE-activity and the maturation of β-amyloid plaques has been
suggested 14. Consequently, the influence and role of BChE in AD and its progress is still under investigation15.
There is growing academic interest in investigating pentacyclic triterpenoic acids as drugs for the treatment of AD in
2

general and for the inhibition of cholinesterases in particular. Triterpenes possessing a hopyl16, lanostyl17 or lupyl18
skeleton were shown to be inhibitors of AChE, and Mehmood et al. extracted triterpenes of the amyryl type that
inhibited BChE on a micro-molar range19. Ursolic acid and its derivatives were determined to be potent cholinesterase
inhibitors18, 20. Especially ursolic acid inhibited AChE in a mixed-type inhibition to an amount being of the same
magnitude as the well-established drug tacrine21. Although glycyrrhetinic acid is well known for its anti-inflammatory22,
23
and anti-viral24, 25 activities, it was unforeseen that this triterpenoid might demonstrate a potential in acting as an
inhibitor of cholinesterases. Glycyrrhizinc acid, the glycone and natural form of glycyrrhetinic acid, was determined to
act as activator of AChE instead of being an inhibitor26. Other oleanolic-type triterpenes were neuroprotective (oleanolic
27
acid) as well as AChE inhibitors (e.g. oleanolic acid28, 29, taraxerol30 or kalopanaxsaponin A/B31) possessing IC50
values comparable to those of donepezil (lancemaside A and echinocystic acid32). Thus, a series of glycyrrhetinic acid
derivatives differing in the substitution pattern at positions C-3 and C-30 were prepared and screened for their inhibitory
action against AChE and BChE using Ellman’s assay. Five representative compounds were selected and investigated for
their ability to act as an inhibitor for the lipase from candida antarctica (a serine hydrolase), papain (a sulfhydryl
enzyme) and carbonic anhydrase II (a metalloenzyme) to gain information about the selectivity of the compounds
towards other enzymes. In addition, preliminary toxicity studies were performed employing murine embryonic
fibroblasts (NiH 3T3) in photometric sulforhodamine B assays (SRB).
2. Results and discussion
2.1. Chemistry
The first group of compounds (1-27, Scheme 1) was synthesized via STEGLICH esterification33 in DCM at room
temperature using boc protected amino acids. These conditions turned out to be appropriate to esterify triterpenoic acids
with amino acids while avoiding an amino acid racemization34. De-protection of these compounds was performed in
almost quantitative yields following standard procedures using either trifluoroacetic acid or a solution of dry hydrogen
chloride in DCM 35, 36
.
Scheme 1. Structure of the aminoacid derivatives 1-27 (Sar corresponds to a sarcosine residue, Dab stands for a 2,4-
diamino-butyric acid moiety).
3

The synthesis of the second group of compounds (28-31, Scheme 2) started from potassium glycyrrhetinate (from the
reaction of glycyrrhetinic acid GA with potassium carbonate in dry DMF) that was treated with an excess of the
respective bromide37, 38. The esters were obtained with yields ranging between 58 % and 79 %.
Likewise, the preparation of the amides (32-36, Scheme 2) was performed starting from glycyrrhetinic acid by its
reaction with DCC and 1-hydroxybenzotriazole in a 2:1-mixture of dry DCM and dry DMF at room temperature37; by
this procedure reasonable yields (up to 54 %) of the products were obtained. Furthermore, the use of an excess of the
respective α,ω-alkyl-diamine allowed a direct coupling without additional protection of position 3.
Scheme 2. Structures glycyrrhetinic acid (GA), esters 28-31 and amides 32-36.
In addition, two derivatives bearing a bulky moiety in position 30 (Scheme 3) were synthesized. Acetylation of GA
gave 3-O-acetyl-GA (AcGA) whose reaction with DCC gave quite nicely the corresponding O-acyl isoureate of 3-
acetyl glycyrrhetinic acid 37. Similarly, the 1H-benzotriazolyl ester (38) could be obtained from GA, DCC and 1-
hydroxybenzotriazol in dry DCM at room temperature; no prior protection of HO-C(3) was required.
Scheme 3. Synthesis of the derivatives 37 and 38: a) DCC, DCM/DMF, r.t., 12 h; b) DCC, 1-hydroxybenzotriazole,
DCM, r.t., 24 h.
4

Compounds 37 and 38 could be characterized by their 1D and 2D 1H and 13C NMR spectra as well as by their ESI mass
spectra (m/z = 719 for 37 and m/z = 587 for 38); the isotopic pattern of the quasimolecular ions agreed perfectly with the
calculated values. Esterification of position 30 resulted in a shift of the signal of C(30) as expected (∆δ = 6 ppm) to
higher fields.
2.2. Biology
Glycyrrhitinic acid, galantamine hydrobromide as well as compounds 1-36 were subjected to Ellman’s assays to
determine their inhibitory activity towards AChE and BChE. The results from these measurements are compiled in
Table 1.
Table 1
Compounds 1-38, except those being not soluble under the conditions of the assay, are competitive inhibitors of AChE
and BChE. For the amino acid substituted derivatives 3-27, inhibition constants as low as Ki = 11.73 1.79 µM
(compound 16) were obtained. Hence, this substance has a 22-times lower activity on AChE than galantamine
possessing a Ki of 0.54 0.01 µM. As compiled in Table 1, many of these aminoacid-derived compounds exhibited
inhibitory constants in double-digit micro-molar range.
For none of the compounds, Ki values smaller than 100 µM could be determined. The selectivity (F) for AChE,
[expressed by the quotient of Ki (AChE) / Ki (BChE)] is similar to galantamine hydrobromide (cf. 16 (F < 0.12) and
galantamine hydrobromide: F = 0.06).
The esters 28-31, representing a second group of compounds, gave similar results. Inhibitory constants of Ki = 13.02 to
29.63 µM for AChE were determined, while no Ki was detectable below 100 µM for BChE. As a consequence,
selectivities ranging between F < 0.74 and F < 0.13 were obtained.
With the exception of 33, none of the compounds of a third group (32-38) showed any remarkable activities for both
enzymes. Compound 33, however, represents the first derivative possessing not only an inhibitory constant in micro-
molar range (5.43 0.91 µM) for BChE, but also a Ki above 100 µM for AChE. Accordingly, selectivity concerning
BChE was established, expressed by a selectivity factor of F > 18.42. While compound 37 was no good inhibitor at all,
38 was the second compound of this series exhibiting an inhibitory constant in the single-digit micro-molar range (Ki =
9.81 0.32 µM) as well as a selectivity of F > 2.04 in favour of BChE.
In addition to these cholinesterase assays, five representative compounds were subjected to assays employing three
other enzymes – the lipase from Candida antarctica, papain from Carica papaya and carbonic anhydrase II from bovine
erythrocytes; each of these enzymes stands for a different mechanism taking place in the active site of the enzyme.
From these experiments some information about the general selectivity of the inhibitors can be expected. Five
derivatives (19, 23, 31, 33 and 38) were selected and tested for their inhibitory action on these enzymes (using a
concentration of 50 µM, except for 38 that was tested using a 10 µM concentration due to its limited solubility). The
results from these studies are compiled in Table 2.
5

Table 2
None of these compounds showed any inhibitory action on papain. Almost the same results were obtained for the
bovine carbonic anhydrase II (bCA II); the compounds did not inhibit this enzyme, except for compounds 23 and 38
being weak inhibitors (15 % inhibition for 23 and 27 % for 38). All of the compounds, however, were inhibitors for the
lipase from C. antarctica. This lipase is a serine hydrolase like the cholinesterases. With exception of compound 31,
inhibition of the fungal lipase was weaker than that of the cholinesterases. Thus, compounds 33 and 38 showed a
reasonably high BChE/lipase and BChE/AChE-selectivity.
The same compounds were subjected to a sulforhodamine B assay using murine embryonic fibroblasts (NiH 3T3) to
obtain IC50 values as an indicator for their cytotoxicity (Table 3).
Table 3
The AChE inhibitors 19, 23 and 31 differ in their cytotoxicity: While compound 23 was not cytotoxic at concentrations
lower than 30 µM (cut-off of the assay), compounds 31 and 19 showed IC50 values in a micro-molar range (for 31: IC50
= 3.05 0.17 µM; for 19: IC50 = 19.73 1.02 µM). Both BChE inhibitors 33 and 38, however, did not show any
cytotoxicity at concentrations lower than 30 µM.
2.3. Docking Studies
In order to have a molecular insight on the mode of action of 33 and 38 as BChE inhibitors and their selectivity towards
AChE we performed in silico molecular docking studies in the active site of both enzymes, using GOLD 5.1 software39.
The coordinates of the enzyme structure were obtained from Protein Data Bank selecting the structures with accession
codes 1P0I and 4BDT, for BChE and AChE, respectively. AChE and BChE have a common catalytic triad, Ser-His-Glu,
and for both enzymes the triad is located at the bottom of a deep and narrow gorge where the Ser residue acts as a
nucleophile to attack the carbonyl groups of substrates or of pseudo-substrate inhibitors40.
6

Figure 1. Illustration of the results from the docking calculations for compounds 33 (A: on the BChE gorge, B: on the
AChE gorge) and 38 (C: on the BChE gorge, D: on the AChE gorge).
The docked poses for compounds 33 and 38 in BChE (A and C Figure 1) and AChE (B and D, Figure 1) showed for
BChE the inhibitors very well accommodated in the enzyme gorge allowing compound 33 (A) to establish an ionic
interaction between the terminal protonated amine with Glu197 and for compound 38 (C) the benzotriazole adopted a
parallel fitting with Trp82 leading to a π-π interaction within the enzyme’s active-site. On the other hand when these
compounds were docked into the AChE active site, the compounds did not fit properly into the AChE gorge. While for
compound 33 (B) the preferred pose sat on the entrance of the gorge and no interactions were observed with important
residues, for compound 38 (D) the benzotriazole moiety was inside the gorge but still no interactions were observed
with essential residues. Hence, the presence of interactions with residues in the bottom of the gorge observed for
compounds 33 and 38 seem mandatory for a better recognition and/or to block the action of the catalytic triad and thus
for an increased inhibitory activity.
3. Conclusions
In this study 36 derivatives of glycyrrhetinic acid, altered in positions 3 and/or 30, were measured in Ellman’s assays
employing acetyl- and butyrylcholinesterases. Nearly half of these compounds exhibited competitive inhibition of either
AChE or BChE showing inhibition constants Ki = 5.4 to 41.8 µM. Two derivatives (33 and 38) inhibited BChE
selectively with Ki = 5.43 µM (for 33) and Ki = 9.81 µM (for 38) as well as selectivity factors of F > 18.42 (for 33) and
F > 2.04 (for 38). Thus, both compounds represent the first derivatives of a triterpenoic acid showing a selective
inhibition of BChE as compared to AChE. Docking studies revealed interactions (for 33: ionic interaction with Glu197,
for 38: π-π interaction with Trp82) between the compounds and the active site of BChE. In addition, both of these
derivatives did not fit properly into the AChE gorge, hence giving an explanation for the observed BChE/AChE
selectivity. Furthermore, 33 and 38 were subjected to three more enzyme assay using bCA II, a lipase and papain. The
results from these experiments emphasized the observed selectivity of compounds for BChE. In addition, neither 33 nor
7

38 showed any cytotoxic effect on NiH 3T3 cells.
In conclusion, glycyrrhetinic acid derivatives represent a novel class of possible cholinesterase inhibitors with
inhibitions constants in the micro-molar range. Two of these compounds were selective BChE inhibitors thus being
possible leads for further investigations and, consequently, for new therapeutic approaches for the treatment of AD.
4. Experimental
4.1. Chemistry
4.1.1 General
Reagents were bought from commercial suppliers without any further purification. NMR spectra were measured on
Varian Gemini 2000 or Unity 500 spectrometers at 27 °C with trimethylsilane as an internal standard, δ are given in
ppm and J in Hertz. Mass spectra were taken on a Finnigan MAT TSQ 7000 (electronspray, voltage 4.5 kV, sheath gas
nitrogen) instrument. IR spectra were recorded on a Perkin–Elmer FT-IR spectrometer Spectrum 1000, optical rotations
on a Perkin–Elmer 341 polarimeter (1 cm micro cell) and UV–vis spectra on a Perkin–Elmer unit, Lambda 14. Melting
points were measured with a Leica hot stage microscope and are uncorrected. Elemental analysis was done on a Foss-
Heraeus Vario EL unit. TLC was performed on silica gel (Merck 5554, detection by UV absorption). Solvents were
dried before use according to usual procedures.
The following compounds were synthesized as previously published: 1 to 638, 7 to 11, 14 and 19 to 2136, 22 to 2735, 31
to 33 and 35 to 3837. The purity of the compounds was checked by HPLC (> 98 %).
4.1.2 General method for esterifications at position C(3) (method A)
The starting material (1 equiv) was dissolved in dry DCM, DMAP (20 mg, 0.16 mmol) and the protected aminoacid
(1.2 equiv) were added. After addition of DCC (1.2 equiv), the mixture was stirred at room temperature for 12 h,
filtered, and the filtrate was washed with water and brine, dried over sodium sulfate, filtered, and the solvents were
evaporated. Purification was performed by flash chromatography (silica gel, chloroform/ether, 9:1).
4.1.3 General method for deprotection (method B)
To a solution of the Boc-protected compound in dry DCM, trifluoroacetic acid (1 mL per 10 mL DCM) was added. The
mixture was allowed to stir at room temperature for 12 h. After completion of the reaction (as monitored by TLC) the
solution was washed with a satd aqueous solution of sodium hydrogen carbonate. The aqueous layer was extracted with
DCM, the combined organic extracts were washed with brine, dried over sodium sulfate, filtrated and evaporated to
yield the amine.
4.1.4 General method for amidation (method C)
GA (1 equiv), DCC (1.1 equiv) and 1-hydroxybenzotriazole (1.2 equiv) were dissolved in 8 mL of dry DMF and stirred
at room temperature for 1 h. The alkyl-1,ω-diamine (2 equiv), dissolved in 1 mL of dry DMF, was added, and stirring at
room temperature was continued for 14 h. The mixture was poured into ice-cooled water; the precipitate was collected,
dried in vacuum and subjected to column chromatography (silica gel, methanol) to yield the product.
8

4.1.5.1. Ethyl (3β) 3-([N-Boc-L-phenylalanyl]oxy)-11-oxo-olean-12-en-30-oate (12)
Compound 12 was obtained from methyl glycyrrhetinate (518 mg, 1.09 mmol) by method A as a colorless powder,
using boc-L-phenylalanine (348 mg, 1.31 mmol) and DCC (270 mg, 1.31 mmol); yield: 769 mg, 99 %; m.p. 90-92 °C;
RF = 0.66 (hexane/ethyl acetate, 7:3); [α]D = 89.08° (c 0.48, CHCl3); UV-Vis (MeOH): λmax (log ε) = 267 nm (4.09); IR
(KBr): ν = 3446 (br), 2976 (s), 1725 (s), 1661 (s), 1498 (m), 1456 (m), 1389 (m), 1366 (m), 1249 (m), 1216 (m), 1173
1
(s), 1086 (w), 1020 (w) cm-1; H NMR (500 MHz, CDCl3): δ = 7.28 (m, 2H, Ph-H-3 and Ph-H-5), 7.22 (m, 1H, Ph-H-
4), 7.17 (m, 2H, Ph-H-2 and Ph-H-5), 5.64 (s, 1H, H-12), 4.88 (d, 1H, Phe-CHNH, J = 8.7 Hz), 4.55 (m, 1H, Phe-
CHNH), 4.52 (dd, 1H, H-3, J = 10.8, 5.6 Hz), 4.18 (dq, 1H, Et-CHH′, J = 10.8, 7.2 Hz), 4.12 (dq, 1H, Et-CHH′, J =
10.8, 7.2 Hz), 3.10 (m, 1H, Phe-CHH′), 3.04 (m, 1H, Phe-CHH′), 2.79 (m, 1H, H-1), 2.34 (s, 1H, H-9), 2.09 (dd, 1H, H-
18, J = 13.3, 3.5 Hz), 2.02 (ddd, 1H, H-15, J = 13.7, 13.7, 4.6 Hz), 1.98 (m, 1H, H-21), 1.92 (ddd, 1H, H-19, J = 13.4,
4.0, 2.7 Hz), 1.81 (ddd, 1H, H-16, J = 13.4, 13.4, 4.3 Hz), 1.62 (m, 1H, H-7), 1.60 (dd, 1H, H-19′, J = 13.4, 13.4 Hz),
1.56 (m, 1H, H-6), 1.42 - 1.37 (br, 3H, H-6′ and H-7′ and H-22), 1.39 (s, 9H, Boc-CH3), 1.35 (s, 3H, H-27), 1.32 (m,
1H, H-22′), 1.31 (m, 1H, H-21′), 1.25 (t, 3H, COOCH2CH3, J = 7.2 Hz), 1.17 (m, 1H, H-16′), 1.13 (s, 6H, H-28 and H-
25), 1.11 (s, 3H, H-26), 1.03 (m, 1H, H-1′), 1.00 (m, 1H, H-15′), 0.80 (s, 3H, H-23), 0.80 (m, 1H, H-5), 0.79 (s, 6H, H-
24 and H-29) ppm; 13C NMR (125 MHz, CDCl3): δ = 200.0 (C-11), 176.3 (C-30), 171.8 (COO), 169.3 (C-13), 155.0
(Boc-COO), 136.1 (Ph-C-1), 129.3 (Ph-C-2, Ph-C-6), 128.6 (C-12), 128.5 (Ph-C-3), 128.4 (Ph-C-5), 126.9 (Ph-C-4),
82.1 (C-3), 79.7 (Boc-q.C), 61.7 (C-9), 60.3 (Et-CH2), 55.0 (C-5), 54.6 (Phe-CHNH), 48.4 (C-18), 45.4 (C-14), 43.8 (C-
20), 43.2 (C-8), 41.0 (C-19), 38.7 (C-1), 38.4 (Phe-CH2), 38.0 (C-10), 37.7 (C-22), 36.9 (C-4), 32.7 (C-7), 31.8 (C-17),
31.1 (C-21), 28.5 (C-29), 28.3 (Boc-CH3), 26.5 (C-16), 26.4 (C-15), 23.4 (C-2), 23.3 (C-27), 18.6 (C-26), 17.3 (C-6),
16.7 (C-24), 16.3 (C-25), 14.3 (Et-CH3) ppm; MS (ESI, MeOH): m/z (%) = 746.1 ([M+H]+, 28), 768.5 ([M+Na]+, 100);
analysis calculated for C46H67NO7 (746.03): C 74.06, H 9.05, N 1.88; found: C 73.91, H 9.14, N 1.72.
4.1.5.2. Ethyl (3β) 3-([L-phenylalanyl]oxy)-11-oxo-olean-12-en-30-oate (13)
Compound 13 was obtained from compound 12 (622 mg, 0.83 mmol) by method B as a colorless powder; yield: 480
mg, 90 %. m.p. 171-175 °C; RF = 0.40 (DCM/MeOH, 9:1); [α]D = 113.50° (c 0.51, CHCl3); UV-Vis (MeOH): λmax (log
ε) = 267 nm (4.07); IR (KBr): ν = 3432 (br), 2950 (s), 2362 (w), 1727 (s), 1655 (s), 1455 (m), 1388 (w), 1324 (w), 1215
1
(m), 1176 (m), 1086 (w), 1021 (w) cm-1; H NMR (400 MHz, CDCl3): δ = 7.28 (m, 2H, Ph-H-2 and Ph-H-6), 7.22 (m,
1H, Ph-H-4), 7.20 (m, 2H, Ph-H-3 and Ph-H-5), 5.63 (s, 1H, H-12), 4.54 (dd, 1H, H-3, J = 11.6, 5.0 Hz), 4.17 (dq, 1H,
Et-CHH′, J = 10.8, 7.1 Hz), 4.11 (dq, 1H, Et-CHH′, J = 10.8, 7.1 Hz), 3.71 (dd, 1H, Phe-CHNH2, J = 8.3, 5.4 Hz), 3.13
(dd, 1H, Phe-CHH′, J = 13.3, 5.4 Hz), 2.80 (m, 1H, H-1), 2.78 (m, 1H, Phe-CHH′), 2.34 (s, 1H, H-9), 2.09 (dd, 1H, H-
18, J = 13.7, 3.3), 2.02 (ddd, 1H, H-15, J = 13.3, 13.3, 4.2 Hz), 1.97 (m, 1H, H-21), 1.91 (ddd, 1H, H-19, J = 13.7, 4.2,
2.5 Hz), 1.81 (ddd, 1H, H-16, J = 13.7, 13.7, 4.6 Hz), 1.69 (m, 1H, H-2), 1.63 (m, 1H, H-7), 1.59 (dd, 1H, H-19′, J =
13.3, 13.3 Hz), 1.57 (m, 1H, H-2′), 1.45 (m, 1H, H-6′), 1.40 (m, 1H, H-7′), 1.37 (m, 1H, H-22), 1.35 (s, 3H, H-27), 1.31
(m, 1H, H-22′), 1.30 (m, 1H, H- 21′), 1.25 (t, 3H, Et-CH3, J = 7.1), 1.16 (m, 1H, H-16′), 1.15 (s, 3H, H-25), 1.13 (s, 3H,
H-28), 1.11 (s, 3H, H-26), 1.04 (ddd, 1H, H-1′, J = 13.7, 13.7, 4.2 Hz), 1.00 (m, 1H, H-15′), 0.85 (s, 3H, H-24), 0.79 (m,
1H, H-5), 0.79 (s, 6H, H-23 and H-29) ppm; 13C NMR (125 MHz, CDCl3): δ = 200.0 (C-11), 176.3 (C-30), 174.7 (Phe-
COO), 169.4 (C-13), 137.5 (Ph-C-1), 129.3 (Ph-C-3 and Ph-C-5), 128.5 (Ph-C-2 and Ph-C-6), 128.4 (C-12), 126.7 (Ph-
C-4), 81.4 (C-3), 61.7 (C-9), 60.3 (Et-CH2), 56.2 (Phe-CNH), 55.0 (C-5), 48.4 (C-18), 45.4 (C-14), 43.8 (C-20), 43.2
(C-8), 41.3 (Phe-CH2), 41.1 (C-19), 38.7 (C-1), 38.1 (C-10), 37.7 (C-22), 36.9 (C-4), 32.7 (C-7), 31.8 (C-17), 31.1 (C-
21), 28.5 (C-29), 28.3 (C-23), 28.0 (C-28), 26.5 (C-16), 26.4 (C-15), 23.5 (C-2), 23.3 (C-27), 18.7 (C-26), 17.3 (C-6),
16.7 (C-24), 16.3 (C-25), 14.3 (Et-CH3) ppm; MS (ESI, MeOH): m/z = 646.5 ([M+H]+, 100); analysis calculated for
9

C41H59NO5 (645.91): C 76.24, H 9.21, N 2.17; found: 76.10, H 9.37, N 2.09.
4.1.5.3. Ethyl (3β) 3-([Boc-D-tryptophanyl]oxy)-11-oxo-olean-12-en-30-oate (15)
Compound 15 was obtained from GA-Et (466 mg, 0.94 mmol) by method A as a colorless powder, using boc-D-
tryptophane (230 mg, 1.13 mmol) and DCC (233 mg, 1.13 mmol); m.p. 106-110 °C; RF = 0.49 (hexane/ethyl acetate,
7:3); [α]D = 98.62° (c 0.52, CHCl3); UV-Vis (MeOH): λmax (log ε) = 241 nm (4.62), 269 nm (4.22); IR (KBr): ν = 3386
(br), 2976 (s), 1726 (s), 1659 (s), 1498 (m), 1458 (m), 1390 (m), 1366 (m), 1251 (m), 1216 (s), 1173 (s), 1086 (m), 1049
1
(m), 1020 (m), 987 (m), 740 (m) cm-1; H NMR (500 MHz, CDCl3): δ = 8.09 (br, 1H, Trp-NH), 7.60 (d, 1H, indole-7, J
= 7.8 Hz), 7.33 (d, 1H, indole-4, J = 8.1 Hz), 7.17 (dd, 1H, indole-5, J = 8.1, 7.8 Hz), 7.10 (dd, 1H, indole-6, J = 7.6,
7.6 Hz), 7.00 (s, 1H, indole-2), 5.63 (s, 1H, H-12), 5.08 (d, 1H, Trp-CHNH, J = 7.7 Hz), 4.65 (m, 1H, Trp-CHNH), 4.45
(dd, 1H, H-3, J = 9.8, 6.7 Hz), 4.18 (dq, 1H, Et-CHH′, J = 10.7, 7.2 Hz), 4.12 (dq, 1H, Et-CHH′, J = 10.7, 7.2 Hz), 3.27
(m, 2H, Trp-CH2), 2.75 (ddd, 1H, H-1, J = 13.4, 3.4, 3.4 Hz), 2.33 (s, 1H, H-9), 2.10 (dd, 1H, H-18, J = 12.9, 3.6 Hz),
2.02 (m, 1H, H-15), 1.99 (m, 1H, H-21), 1.92 (ddd, 1H, H-19, J = 13.6, 3.8, 2.5 Hz), 1.81 (ddd, 1H, H-16, J = 13.7,
13.7, 4.6 Hz), 1.64 (m, 1H, H-7), 1.60 (dd, 1H, H-19′, J = 13.5, 13.5 Hz), 1.52 (m, 1H, H-6), 1.50 (m, 1H, H-2), 1.43 (s,
12H, Boc-CH3 and H-28), 1.41 (m, 1H, H-6′), 1.38 (m, 1H, H-7′), 1.36 (m, 1H, H-22), 1.35 (s, 3H, H-27), 1.34 (m, 1H,
H- 22′), 1.30 (m, 1H, H-21′), 1.26 (t, 3H, Et-CH3, J = 7.2), 1.17 (m, 1H, H-16′), 1.14 (s, 3H, H-23), 1.11 (s, 6H, H-25
and H-26), 1.00 (m, 1H, H-15′), 0.98 (m, 1H, H-1′), 0.80 (s, 3H, H-29), 0.79 (m, 1H, H-5), 0.77 (s, 3H, H-24) ppm; 13C
NMR (125 MHz, CDCl3): δ = 200.1 (C-11), 176.4 (C-30), 172.1 (Trp-COO), 169.5 (C-13), 153.1 (Boc-COO), 136.1
(indole-q.C), 128.4 (C-12), 128.3 (indole-q.C), 122.6 (indole-2), 122.1 (indole-5), 119.5 (indole-6), 119.1 (indole-7),
111.0 (indole-4), 110.5 (indole-q.C), 81.9 (C-3), 79.6 (Boc-q.C), 61.6 (C-9), 60.4 (Et-CH2), 55.0 (C-5), 54.3 (Trp-
CHNH), 48.4 (C-18), 45.4 (C-14), 43.8 (C-20), 43.2 (C-8), 41.0 (C-19), 38.6 (C-1), 38.0 (C-10), 37.7 (C-22), 36.8 (C-
4), 32.6 (C-7), 31.8 (C-17), 31.1 (C-21), 28.5 (C-29), 28.3 (C-28), 28.3 (C-23), 27.9 (Trp-CH2), 26.4 (C-16), 26.4 (C-
15), 23.3 (C-27), 23.2 (C-2), 18.6 (C-26), 17.3 (C-6), 16.5 (C-24), 16.3 (C-25), 14.3 (Et-CH3) ppm; MS (ESI, MeOH):
m/z = 785.3 ([M+H]+, 23), 807.3 ([M+Na]+, 100); analysis calculated for C48H68N2O7 (785.06): C 73.44, H 8.73, N
3.57; found: 72.29, H 8.91, N 3.42.
4.1.5.4. Ethyl (3β) 3-([D-tryptophanyl]oxy)-11-oxo-olean-12-en-30-oate (16)
Compound 16 was obtained from compound 15 (127 mg, 0.16 mmol) by method B as a colorless powder; yield: 105
mg, 96 %. m.p. 91-95 °C; RF = 0.37 (DCM/MeOH, 9:1); [α]D = 96.48° (c 0.61, CHCl3); UV-Vis (MeOH): λmax (log ε) =
226 nm (4.62), 240 nm (4.61), 266 nm (4.18); IR (KBr): ν = 3407 (br), 2950 (s), 1727 (s), 1658 (s), 1458 (m), 1388 (m),
1280 (w), 1215 (s), 1176 (m), 1087 (m), 1020 (w) cm-1; 1H NMR (500 MHz, CDCl3): δ = 8.21 (s, 1H, Trp-NH), 7.61 (d,
1H, indole-7, J = 7.7 Hz), 7.35 (d, 1H, indole-4, J = 7.9 Hz), 7.18 (m, 1H, indole-5), 7.12 (m, 1H, indole-6), 7.09 (s, 1H,
indole-2), 5.64 (s, 1H, H-12), 4.50 (dd, 1H, H-3, J = 11.4, 5.0 Hz), 4.18 (dq, 1H, Et-CHH′, J = 10.9, 7.1 Hz), 4.12 (dq,
1H, Et-CHH′, J = 10.9, 7.1 Hz), 3.89 (m, 1H, Trp-CHNH2), 3.31 (dd, 1H, Trp-CHH′, J = 14.9, 4.6 Hz), 3.09 (dd, 1H,
Trp-CHH′, J = 14.8, 7.8 Hz), 2.78 (ddd, 1H, H-1, J = 13.6, 3.7, 3.7 Hz), 2.42 (br, 2H, NH2), 2.34 (s, 1H, H-9), 2.10 (dd,
1H, H-18, J = 13.6, 3.8 Hz), 2.03 (m, 1H, H-15), 1.99 (m, 1H, H-21), 1.92 (ddd, 1H, H-19, J = 13.4, 3.9, 2.7 Hz), 1.82
(ddd, 1H, H-16, J = 13.7, 13.7, 4.2 Hz), 1.65 (m, 1H, H-7), 1.63 (m,1H, H-2), 1.61 (dd, 1H, H-19′, J = 13.6, 13.6 Hz),
1.59 (m, 1H, H-2′), 1.56 (m, 1H, H-6), 1.43 (m, 1H, H-6′), 1.40 (m, 1H, H-7′), 1.38 (m, 1H, H-22), 1.36 (s, 3H, H-27),
1.34 (m, 1H, H-22′), 1.31 (m, 1H, H-21′), 1.26 (t, 3H, Et-CH3, J = 7.1 Hz), 1.17 (m, 1H, H-16′), 1.14 (s, 3H, H-28), 1.13
(s, 3H, H-25), 1.11 (s, 3H, H-26), 1.02 (m, 1H, H-15′), 1.00 (m, 1H, H-1′), 0.83 (s, 3H, H-24), 0.82 (s, 3H, H-23), 0.80
(s, 3H, H-29), 0.79 (m, 1H, H-5) ppm; 13C NMR (125 MHz, CDCl3): δ = 200.0 (C-11), 176.4 (C-30), 169.4 (C-13),
10

136.3 (indole-q.C), 128.4 (C-12), 127.4 (indole-q.C), 123.3 (indole-2), 122.2 (indole-5), 119.5 (indole-6), 118.8 (indole-
7), 111.2 (indole-4), 110.5 (indole-q.C), 81.9 (C-3), 61.6 (C-9), 60.3 (Et-CH2), 55.0 (C-5), 54.8 (Trp-CHNH), 48.4 (C-
18), 45.4 (C-14), 43.8 (C-20), 43.2 (C-8), 41.1 (C-19), 38.7 (C-1), 38.1 (C-10), 37.7 (C-22), 36.9 (C-4), 32.6 (C-7), 31.8
(C-17), 31.1 (C-21), 30.0 (Trp-CH2), 28.5 (C-29), 28.3 (C-28), 28.0 (C-23), 26.5 (C-16), 26.4 (C-15), 23.3 (C-27), 23.3
(C-2), 18.6 (C-26), 17.3 (C-6), 16.6 (C-24), 16.3 (C-25), 14.3 (Et-CH3) ppm; MS (ESI, MeOH): m/z = 685.3 ([M+H]+,
100); analysis calculated for C43H60N2O5 (684.95): C 75.40, H 8.83, N 4.09; found: C 75.26, H 8.99, N 3.87.
4.1.5.5. Methyl (3β) 3-([S-benzyl-N-boc-L-cysteinyl]oxy)-11-oxo-olean-12-en-30-oate (17)
Compound 17 was obtained from methyl glycyrrhetinate (730 mg, 1.51 mmol) by method A as a colorless powder,
using S-benzyl-N-boc-L-cysteine (562 mg, 1.81 mmol) and DCC (373 mg, 1.81 mmol); yield: 670 mg, 57 %. m.p. 112-
115 °C; RF = 0.64 (hexane/ethyl acetate, 7:3); [α]D = 57.94° (c 0.43, CHCl3); UV-vis (MeOH): λmax (log ε) = 248 nm
(4.01); IR (KBr): ν = 3329 (br), 2930 (s), 2852 (m), 1719 (s), 1654 (s), 1627 (s), 1576 (m), 1508 (m), 1455 (m), 1390
(m), 1367 (m), 1341 (m), 1246 (m), 1216 (s), 1167 (s), 1088 (w), 1063 (w) cm-1; 1H NMR (500 MHz, CDCl3): δ = 7.32-
7.20 (br, 5H, H-Ar), 5.67 (s, 1H, H-12), 5.29 (d, 1H, NH, J = 7.9), 4.57 (dd, 1H, H-3, J = 11.7, 4.8 Hz), 4.51 (m, 1H,
Cys-CHNH), 3.75 (s, 2H, Bn-CH2), 3.69 (s, 3H, OCH3), 2.88 (m, 1H, Cys-CHH′), 2.84 (m, 1H, Cys-CHH′), 2.82 (m,
1H, H-1), 2.35 (s, 1H, H-9), 2.09 (dd, 1H, H-18, J = 13.5, 3.5 Hz), 2.03 (m, 1H, H-15), 1.99 (m, 1H, H-21), 1.93 (m,
1H, H-19), 1.83 (ddd, 1H, H-16, J = 13.7, 13.7, 3.7 Hz), 1.74 (m, 1H, H-2), 1.72 (m, 1H, H-7), 1.66 (m, 1H, H-6), 1.64
(m, 1H, H-2′), 1.61 (dd, 1H, H-19′, J = 13.6, 13.6 Hz), 1.58 (m, 1H, H-6′), 1.46 (s, 9H, Boc-CH3), 1.43 (m, 1H, H-7′),
1.38 (m, 1H, H-22), 1.36 (s, 3H, H-27), 1.31 (m, 1H, H-22′), 1.31 (m, 1H, H-21′), 1.18 (m, 1H, H-16′), 1.16 (s, 3H, H-
25), 1.15 (s, 3H, H-29), 1.13 (s, 3H, H-26), 1.08 (m, 1H, H-15′), 1.02 (m, 1H, H-1′), 0.87 (s, 3H, H-23), 0.85 (s, 3H, H-
24), 0.81 (s, 3H, H-28), 0.79 (m, 1H, H-5) ppm; 13C NMR (125 MHz, CDCl3): δ = 200.0 (C-11), 176.9 (C-30), 170.8
(Cys-COO), 169.3 (C-13), 157.6 (Boc-COO), 137.7 (Car), 130.1 (Car), 128.9 (Car), 128.6 (Car), 128.5 (C-12), 128.4 (Car),
127.1 (Car), 82.4 (C-3), 79.7 (Boc-q.C), 61.6 (C-9), 55.0 (C-5), 53.5 (Cys-CHNH), 51.7 (OCH3), 48.4 (C-18), 45.4 (C-
8), 44.0 (C-20), 43.2 (C-14), 41.1 (C-19), 38.7 (C-1), 38.1 (C-4), 37.7 (C-22), 36.9 (C-10), 36.8 (Bn-CH2), 33.7 (Cys-
CH2), 32.6 (C-7), 31.8 (C-17), 31.1 (C-21), 28.5 (C-28), 28.3 (Boc-CH3), 28.3 (C-29), 28.1 (C-23), 26.4 (C-16), 26.4
(C-15), 23.5 (C-2), 23.3 (C-27), 18.7 (C-26), 17.3 (C-6), 16.7 (C-24), 16.3 (C-25) ppm; MS (ESI): m/z (%) = 778.1
([M+H]+, 10), 795.3 ([M+NH4]+, 11), 800.4 ([M+Na]+, 100), 816.3 ([M+K]+, 20), 832.7 ([M+Na+MeOH]+, 13), 1189.7
([3M+2Na]2+, 12), 1578.3 ([2M+H+Na]+, 20); analysis calculated for C46H67NO7S (778.09): C 71.01, H 8.68, N 1.80;
S, 4.12; found: C 70.86, H 8.74, N 1.69, S 3.98.
4.1.5.6. Methyl (3β) 3-([S-benzyl-L-cysteinyl]oxy)-11-oxo-olean-12-en-30-oate (18)
Compound 18 was obtained from compound 16 (190 mg, 0.24 mmol) by method B as a colorless powder, using
trifluoroacetic acid (1 mL, 12.98 mmol); yield: 140 mg, 86 %. m.p. 128-131 °C; RF = 0.66 (CHCl3/MeOH, 9:1); [α] =
62.38° (c 0.43, CHCl3); UV-vis (MeOH): λmax (log ε) = 249 nm (4.31); IR (KBr): ν = 3406 (br), 2929 (s), 1732 (s), 1660
1
(s), 1570 (w), 1454 (m), 1387 (m), 1324 (w), 1217 (s), 1155 (m), 1087 (w), 1028 (w) cm-1; H NMR (500 MHz,
CDCl3): δ = 7.36-7.20 (m, 5H, H-Ar), 5.66 (s, 1H, H-12), 4.58 (dd, 1H, H-3, J = 11.8, 4.7 Hz), 3.93 (m, 1H, Cys-
CHNH), 3.82 (s, 2H, Bn-CH2), 3.69 (s, 3H, OCH3), 3.02 (dd, 1H, Cys-CHH′, J = 13.9, 4.4 Hz), 2.91 (dd, 1H, Cys-
CHH′, J = 13.9, 7.1 Hz), 2.81 (m, 1H, H-1), 2.34 (s, 1H, H-9), 2.09 (dd, 1H, H-18, J = 13.5, 3.7 Hz), 2.03 (m, 1H, H-
15), 1.99 (m, 1H, H-21), 1.93 (m, 1H, H-19), 1.82 (ddd, 1H, H-16, J = 13.5, 13.5, 3.9 Hz), 1.71 (m, 1H, H-2), 1.68 (m,
1H, H-7), 1.66 (m, 1H, H-6), 1.63 (m, 1H, H-2′), 1.61 (dd, 1H, H-19′, J = 13.5, 13.5 Hz), 1.56 (m, 1H, H-6′), 1.42 (m,
1H, H-7′), 1.38 (m, 1H, H-22), 1.36 (s, 3H, H-27), 1.31 (m, 1H, H-22′), 1.31 (m, 1H, H-21′), 1.18 (m, 1H, H-16′), 1.15
11

(s, 3H, H-25), 1.15 (s, 3H, H-29), 1.12 (s, 3H, H-26), 1.09 (m, 1H, H-15′), 1.02 (m, 1H, H-1′), 0.85 (s, 3H, H-23), 0.83
(s, 3H, H-24), 0.81 (s, 3H, H-28), 0.77 (m, 1H, H-5) ppm; 13C NMR (125 MHz, CDCl3): δ = 199.8 (C-11), 176.9 (C-
30), 169.2 (Cys-COO), 169.2 (C-13), 137.6 (Car), 129.0 (Car), 129.0 (Car), 128.6 (Car), 128.5 (C-12), 128.5 (Car), 127.2
(Car), 83.1 (C-3), 61.6 (C-9), 55.0 (C-5), 51.7 (OCH3), 49.2 (Cys-CHNH), 48.4 (C-18), 45.4 (C-8), 44.0 (C-20), 43.2 (C-
14), 41.1 (C-19), 38.6 (C-1), 38.1 (C-4), 37.7 (C-22), 36.9 (C-10), 36.7 (Bn-CH2), 33.9 (Cys-CH2), 32.6 (C-7), 31.8 (C-
17), 31.1 (C-21), 28.5 (C-28), 28.3 (C-29), 28.2 (C-23), 26.4 (C-16), 26.4 (C-15), 23.5 (C-2), 23.4 (C-27), 18.7 (C-26),
17.3 (C-6), 16.8 (C-24), 16.3 (C-25) ppm; MS (ESI): m/z (%) = 678.3 ([M+H]+, 100), 1017.2 ([3M+2H]2+, 6), 1355.6
([2M+H]+, 2); analysis calculated for C41H59NO5S (677.98): C 72.63, H 8.77, N 2.07; S, 4.73; found: c 72.57, H 8.96,
N 1.94, S 4.57.
4.1.5.9. (3β) N-(2-Aminoethyl) 3-hydroxy-11-oxo-olean-12-en-30-amide (32)
Compound 32 was obtained from GA (400 mg, 0.85 mmol) by method C as a colorless powder, using DCC (194 mg,
0.94 mmol), 1-hydroxybenzotriazole (138 mg, 1.02 mmol) and 1,2-diaminoethane (102 mg, 1.70 mmol); yield: 150 mg,
34 %. m.p. 193-199°C (decomp.); RF = 0.05 (MeOH/CHCl3, 8:2); [α]D = 82.93° (c 0.34, MeOH); UV-vis (MeOH): λmax
(log ε) = 249 nm (3.77); IR (KBr): ν = 3403 (br), 2950 (m), 2870 (m), 1642 (s), 1534 (m), 1384 (s), 1040 (w), 994 (w),
826 (w), 726 (w), 668 (m), 590 (m), 544 (m) cm-1; 1H NMR (500 MHz, MeOH-d4): δ = 5.62 (s, 1H, H-12), 3.46 (m, 2H,
chain-1-CH2), 3.17 (dd, 1H, H-3, J = 11.8, 4.5 Hz), 3.03 (dd, 2H, chain-2-CH2, J = 6.6, 6.6 Hz), 2.72 (ddd, 1H, H-1, J =
13.3, 3.3, 3.3 Hz), 2.46 (s, 1H, H-9), 2.16 (m, 1H, H-15), 2.15 (dd, 1H, H-18, J = 13.4, 4.0 Hz), 1.93 (m, 1H, H-21),
1.88 (m, 1H, H-19), 1.88 (m, 1H, H-16), 1.74 (m, 1H, H-19′), 1.72 (m, 1H, H-7), 1.67 (m, 1H, H-2), 1.63 (m, 1H, H-6),
1.54 (m, 1H, H-2′), 1.49 (m, 1H, H-21′), 1.47 (m, 1H, H-6′), 1.45 (m, 1H, H-7′), 1.43 (s, 3H, H-27), 1.42 (m, 1H, H-22),
1.37 (m, 1H, H-22′), 1.25 (m, 1H, H-16′), 1.15 (s, 3H, H-29), 1.14 (s, 3H, H-25), 1.14 (s, 3H, H-26), 1.04 (m, 1H, H-
15′), 1.02 (m, 1H, H-1′), 1.00 (s, 3H, H-23), 0.83 (s, 3H, H-28), 0.80 (s, 3H, H-24), 0.77 (m, 1H, H-5) ppm; 13C NMR
(100 MHz, MeOH-d4): δ = 202.7 (C-11), 180.3 (C-30), 172.6 (C-13), 129.0 (C-12), 79.4 (C-3), 63.2 (C-9), 56.2 (C-5),
49.7 (C-18), 46.7 (C-8), 44.8 (C-20), 44.6 (C-14), 42.5 (C-19), 40.8 (chain-2), 40.3 (C-1), 40.2 (C-4), 38.7 (C-22), 38.7
(chain-1), 38.3 (C-10), 33.8 (C-7), 32.9 (C-17), 31.9 (C-21), 29.5 (C-29), 29.1 (C-28), 28.7 (C-23), 27.8 (C-2), 27.6 (C-
16), 27.4 (C-15), 23.8 (C-27), 19.3 (C-26), 18.6 (C-6), 16.9 (C-25), 16.3 (C-24) ppm; MS (ESI): m/z (%) = 513.5
([M+H]+, 100), 1025.6 ([2M+H]+, 3); analysis calculated for C32H52N2O3 (512.77): C 74.95, H 10.22, N 5.46; found: C
74.79, H10.37, N 5.31.
4.1.5.10. (3β) N-(5-Aminopentyl) 3-hydroxy-11-oxo-olean-12-en-30-amide (36)
Compound 34 was obtained from GA (400 mg, 0.85 mmol) by method C as a colorless powder, using DCC (194 mg,
0.94 mmol), 1-hydroxybenzotriazole (138 mg, 1.02 mmol) and 1,2-diaminopentane (174 mg, 1.70 mmol); yield: 165
mg, 35 %. m.p. 187-192°C (decomp.); RF = 0.05 (MeOH/CHCl3, 8:2); [α]D = 94.12° (c 0.52, MeOH); UV-vis (MeOH):
λmax (log ε) = 249 nm (3.89); IR (KBr): ν = 3424 (br), 2946 (m), 2868 (w), 1638 (m), 1540 (w), 1384 (s), 1214 (w),
1
1040 (w) cm-1; H NMR (500 MHz, MeOH-d4): δ = 5.61 (s, 1H, H-12), 3.27 (m, 1H, chain-1-CHH′), 3.20 (m, 1H,
chain-1-CHH′) 3.17 (m, 1H, H-3), 2.94 (m, 2H, chain-5-CH2), 2.71 (ddd, 1H, H-1, J = 13.3, 3.4, 3.4 Hz), 2.46 (s, 1H,
H-9), 2.17 (m, 1H, H-15), 2.13 (m, 1H, H-18), 1.96 (m, 1H, H-21), 1.90 (m, 1H, H-19), 1.88 (m, 1H, H-16), 1.74 (m,
1H, H-19′), 1.74 (m, 1H, H-7), 1.70 (m, 2H, chain-4-CH2), 1.67 (m, 1H, H-2), 1.63 (m, 1H, H-6), 1.57 (m, 2H, chain-2-
CH2) 1.55 (m, 1H, H-2′), 1.49 (m, 1H, H-6′), 1.45 (m, 1H, H-7′), 1.43 (m, 1H, H-21′), 1.43 (s, 3H, H-27), 1.42 (m, 2H,
chain-3-CH2), 1.42 (m, 2H, H-22 and H-22′), 1.25 (m, 1H, H-16′), 1.14 (s, 3H, H-25), 1.14 (s, 3H, H-26), 1.12 (s, 3H,
H-29), 1.05 (m, 1H, H-15′), 1.02 (m, 1H, H-1′), 1.00 (s, 3H, H-23), 0.82 (s, 3H, H-28), 0.80 (s, 3H, H-24), 0.77 (m, 1H,
12

H-5) ppm; 13C NMR (100 MHz, MeOH-d4): δ = 202.6 (C-11), 178.8 (C-30), 172.7 (C-13), 128.9 (C-12), 79.3 (C-3),
63.1 (C-9), 56.1 (C-5), 49.9 (C-18), 46.7 (C-8), 44.8 (C-20), 44.6 (C-14), 42.6 (C-19), 40.7 (chain-5), 40.3 (C-1), 40.2
(C-4), 39.9 (chain-1), 38.8 (C-22), 38.3 (C-10), 33.8 (C-7), 32.9 (C-17), 31.9 (C-21), 30.1 (chain-2), 29.5 (C-29), 29.3
(C-28), 28.7 (C-23), 28.1 (chain-4), 27.8 (C-2), 27.6 (C-16), 27.4 (C-15), 24.8 (chain-3), 23.7 (C-27), 19.3 (C-26), 18.6
(C-6), 16.9 (C-25), 16.3 (C-24) ppm; MS (ESI): m/z (%) = 555.5 ([M+H]+, 100), 1109.5 ([2M+H]+, 2); analysis
calculated for C35H58N2O3 (554.85): C 75.76, H 10.54, N 5.05; found: C 75.51, H 10.65, N 4.98.
4.1.5.7. (Cyclohexylamino)-(cyclohexylimino)-methyl (3β) 3-acetyloxy-11-oxo-olean-12-en-30-oate (37)
3β-Acetyloxy-11-oxo-olean-12-en-30-oic acid (400 mg, 0.78 mmol) was dissolved in a mixture of dry DMF (10 mL)
and dry dichloromethane (15ml) and DCC (270 mg, 0.82 mmol) was added. After 12 h of continous stirring at room
temperature, the solvents were removed under reduced pressure, and the residue was dissolved in mixture of
dichlormethane and water (20 mL, 1:1). The mixture was extracted with dichloromethane (3 x 15 mL), the combined
organic layers were washed with brine (10 mL), dried (Na2SO4), filtered and evaporated. The residue was subjected to
column chromatography (silica gel, hexane/ethyl acetate, 7:3) to yield 37 (280 mg, 50 %) as a colorless powder. m.p.
141-145 °C; RF = 0.18 (hexane/ethyl acetate, 8:2); [α]D = 83.43° (c 0.58, CHCl3); UV-Vis (MeOH): λmax (log ε) = 269
nm (4.10); IR (KBr): ν = 3360 (br), 2932 (s), 2856 (s), 2669 (m), 1740 (s), 1700 (s), 1660 (s), 1509 (s), 1453 (s), 1374
1
(s), 1343 (s), 1320 (s), 1246 (s), 1153 (s), 1085 (m), 1029 (s), 1001 (m), 985 (s) cm-1; H NMR (500 MHz, CDCl3): δ =
5.74 (s, 1H, H-12), 5.49 (d, 1H, NH, J = 7.9 Hz), 4.51 (dd, 1H, H-3, J = 11.7, 4.4 Hz), 4.25 (dddd, 1H, imino-CH, J =
11.8, 11.8, 3.1, 3.1 Hz), 3.66 (br, 1H, amino-CH), 2.78 (ddd, 1H, H-1, J = 13.5, 3.1, 3.1 Hz), 2.34 (s, 1H, H-9), 2.15 (dd,
1H, H-18, J = 12.3, 3.7 Hz), 2.08 (m, 1H, H-19), 2.06 (m, 1H, H-21), 2.04 (s, 3H, Ac-CH3), 2.03-1.94 (br, 4H, 2×CH2
cyclo), 1.72 (ddd, 1H, H-16, J = 11.7, 3.3, 3.3 Hz), 1.84-1.52 (br, 15H, H-2 and H-2′ and H-15 and H-7 and H-21′ and
H-6 and H-19′ and 5 × CH2 cyclo), 1.39-1.30 (br, 10H, H-6′ and H-7′ and H-22 and H-22′ and 3×CH2 cyclo), 1.35 (s,
3H, H-27), 1.28 (s, 3H, H-23), 1.19 (m, 1H, H-16′), 1.11 (m, 1H, H-15′), 1.16 (s, 3H, H-25), 1.12 (s, 3H, H-26), 1.07
(m, 1H, H-1′), 0.87 (s, 3H, H-24), 0.87 (s, 3H, H-28), 0.80 (m, 1H, H-5), 0.80 (s, 3H, H-29) ppm; 13C NMR (125 MHz,
CDCl3): δ = 199.8 (C-11), 175.4 (C-30), 170.9 (Ac-CO), 168.9 (C-13), 154.5 (C=N), 128.6 (C-12), 80.6 (C-3), 61.6 (C-
9), 55.6 (CHN=), 55.0 (C-5), 50.3 (CHNH), 48.2 (C-18), 45.3 (C-20), 43.8 (C-19), 43.2 (C-14), 43.2 (C-8), 38.8 (C-1),
38.4 (C-22), 38.0 (C-10), 36.9 (C-4), 32.8 (C-7), 32.6 (CH2 cyclo), 32.5 (CH2 cyclo), 31.9 (C-17), 31.6 (CH2 cyclo),
31.6 (CH2 cyclo), 30.9 (C-21), 28.7 (C-28), 28.6 (C-29), 28.0 (C-23), 27.0 (CH2 cyclo), 27.0 (CH2 cyclo), 26.7 (C-16),
26.4 (C-15), 26.2 (CH2 cyclo), 25.5 (CH2 cyclo), 25.3 (CH2 cyclo), 24.7 (CH2 cyclo), 23.5 (C-2), 23.0 (C-27), 21.3 (Ac-
Me), 18.6 (C-26), 17.4 (C-6), 16.7 (C-24), 16.4 (C-25); MS (ESI, MeOH): m/z = 719.4 ([M+H]+, 34), 741.5 ([M+Na]+,
100), 1460.4 ([2M+Na]+, 42); analysis calculated for C45H70N2O5 (719.05): C 75.17, H 9.81, N 3.90; found: C 74.14, H
10.01, N 3.87.
4.1.5.8. 1H-Benzotriazol-1-yl (3β) 3-hydroxy-11-oxo-olean-12-en-30-oate (38)
To a solution of GA (500 mg, 1.06 mmol) and 1-hydroxybenzotriazole (157 mg, 1.19 mmol) in dry dichloromethane
(40 mL), DCC (240 mg, 1.17 mmol) was added. After continous stirring at room temperature for 24 h, the mixture was
filtered, and the filtrate was washed with hydrochloric acid (1 M, 20 mL). The mixture was extracted with
dichlormethane (3 x 20 mL), the combined organic layers were washed with brine (20 mL), dried (Na2SO4), filtered and
evaporated to dryness. The residue was subjected to column chromatography (silica gel, hexane/ethyl acetate, 1:1) to
yield 38 (170 mg, 27 %) as a colorless powder. m.p. 192-195 °C (decomp.); RF = 0.13 (hexane/ethyl acetate, 5:3); [α]D
= 120.21° (c 0.32, CHCl3); UV-Vis (MeOH): λmax (log ε) = 214 nm (4.48), 269 nm (4.12); IR (KBr): ν = 3619 (br),
13

3328 (s), 2931 (s), 2851 (s), 1795m, 1655 (s), 1626 (s), 1576m, 1535 (w), 1445 (w), 1387 (w), 1312 (w), 1266 (w),
1244 (w), 1203 (w), 1090 (m), 1036 (m), 1014 (m) cm-1; 1H NMR (500 MHz, CDCl3): δ = 8.08 (m, 1H, H-Ar), 7.56 (m,
1H, H-Ar.), 7.43 (m, 1H, H-Ar.), 7.33 (m, 1H, H-Ar.), 5.70 (s, 1H, H-12), 4.52 (dd, 1H, J = 10.7, 5.5 Hz), 3.22 (dd, 1H,
H-3, J = 10.7, 5.5 Hz), 2.77 (ddd, 1H, H-1, J = 13.5, 3.3, 3.3 Hz), 2.35 (dd, 1H, H-18, J = 13.0, 3.9 Hz), 2.34 (s, 1H, H-
9), 2.27 (ddd, 1H, H-21, J = 10.3, 2.8, 2.8 Hz), 2.15 (ddd, 1H, H-19, J = 13.9, 3.9, 3.0 Hz), 2.09 (ddd, 1H, H-15, J =
13.9, 13.9, 4.2 Hz), 1.87 (dd, 1H, H-19′, J = 13.9, 13.9 Hz), 1.70 (ddd, 1H, H-16, J = 13.6, 3.9, 3.9 Hz), 1.69 (m, 1H, H-
7), 1.65-1.59 (br, 4H, H-6 and H-22 and H-21′ and H-16′), 1.57 (s, 3H, H-23), 1.46 (m, 1H, H-6′), 1.43 (m, 1H, H-7′),
1.41 (s, 3H, H-27), 1.34 (m, 1H, H-15′), 1.28 (m, 1H, H-2), 1.16 (m, 1H, H-2′), 1.15 (s, 3H, H-26), 1.13 (s, 3H, H-25),
1.01 (s, 3H, H-29), 0.98 (m, 1H, H-1′), 0.94 (s, 3H, H-28), 0.81 (s, 3H, H-24), 0.70 (m, 1H, H-5) ppm; 13C NMR (125
MHz, CDCl3): δ = 199.7 (C-11), 172.4 (C-30), 167.4 (C-13), 143.6 (Car), 129.1 (Car), 128.7 (Car), 128.6 (Car), 124.8
(Car), 120.7 (Car), 128.8 (C-12), 78.8 (C-3), 61.9 (C-9), 55.0 (C-5), 48.3 (C-18), 45.4 (C-8), 44.4 (C-20), 43.2 (C-14),
41.0 (C-19), 39.2 (C-1), 39.2 (C-4), 37.8 (C-22), 37.2 (C-10), 32.8 (C-7), 32.0 (C-17), 31.3 (C-21), 28.6 (C-28), 28.1
(C-29), 28.1 (C-23), 27.4 (C-2), 26.5 (C-16), 25.6 (C-15), 23.5 (C-27), 18.8 (C-26), 17.5 (C-6), 16.4 (C-25), 15.6 (C-24)
ppm; MS (ESI, MeOH): m/z = 588.5 ([M+H]+, 10), 610.4 ([M+Na]+, 100), 626.4 ([M+K]+, 6), 1175.2 ([2M+H]+, 8),
1197.2 ([2M+Na]+, 64), 1213.2 ([2M+K]+, 2); analysis calculated for C36H49N3O4 (587.79): C 73.56, H 8.40, N 7.15;
found: C 73.38, H 8.57, N 6.97.
4.2. Biology
4.2.1. Cell lines and Culture Conditions
The NiH3T3 cells were included in this study. Cultures were maintained as monolayer in RPMI 1640 (PAA
Laboratories, Pasching, Germany) supplemented with 10 % heat inactivated fetal bovine serum (Biochrom AG, Berlin,
Germany) and penicillin / streptomycin (PAA Laboratories) at 37 °C in a humidified atmosphere of 5 % CO2 / 95 % air.
4.2.2. Cytotoxicity Assay41
The cytotoxicity of the compounds was evaluated using the sulforhodamine-B (SRB) (Sigma Aldrich) microculture
colorimetric assay. In short, exponentially growing cells were seeded into 96-well plates on day 0 at the appropriate cell
densities to prevent confluence of the cells during the period of experiment. After 24 h, the cells were treated with serial
dilutions of the compounds (0-30 µM) for 96 h. The final concentration of DMSO or DMF solvent never exceeded 0.5
%, which was non-toxic to the cells. The percentages of surviving cells relative to untreated controls were determined
96 h after the beginning of drug exposure. After a 96 h treatment, the supernatant medium from the 96 well plates was
discarded, and the cells were fixed with 10 % TCA. For a thorough fixation, the plates were allowed to rest at 4 °C.
After fixation, the cells were washed in a strip washer. The washing was done four times with water using alternate
dispensing and aspiration procedures. The plates were then dyed with 100 µl of 0.4 % SRB (sulforhodamine B) for
about 20 min. After dying the plates were washed with 1 % acetic acid to remove the excess of the dye and allowed to
air dry overnight. 100 µl of 10 mM Tris base solution were added to each well and absorbance was measured at λ = 570
nm (using a 96 well plate reader, Tecan Spectra, Crailsheim, Germany). The IC50 was estimated by linear regression
between the value before and after the 50 % line is crossed in a dose-response curve.
4.2.3. Enzymatic Studies
14

4.2.3.1. Spectrophometer and Chemicals
A TECAN SpectraFluorPlus working on the kinetic mode and measuring the absorbance at λ = 415 nm was used for the
enzymatic studies. Acetylcholinesterase (from electrophorus electricus), Papain (from carica papaya), Lipase (from
candida antarctica), 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB) and acetylthiocholine iodide were purchased from
Fluka. Butyrylcholinesterase (from equine serum), carbonic anhydrase II (from bovine erythrocytes) as well as 4-
nitrophenyl acetate (4-NA) were purchased from Sigma and butyrylthiocholine idioide was bought from Aldrich.
4.2.3.2. Solutions Preparation
Preparation of 50 mM Tris-HCl buffer solutions: Tris(hydroxymethyl)-aminomethan (606 mg) was dissolved in bi-
distilled water (100 mL) and adjusted with HCl to a pH of 8.0 0.1 (for AChE, BChE, bCA II and Lipase) and 6.2 0.1
(for Papain), respectively. Buffers was freshly prepared and stored in the refrigerator. AChE solution 2.005 U/ml: the
enzyme (271 U/mg, 0.037 mg) was dissolved in freshly prepared buffer pH 8.0 (5 mL) containing NaN3 (0.98 mg).
BChE solution 2.040 U/ml: the enzyme (7.54 U/mg, 1.353 mg) was dissolved in freshly prepared buffer pH 8.0 (5 mL)
containing NaN3 (0.98 mg). bCA II solution 798 W/A-units/ml: the enzyme (≥3,000 W-A units/mg, 0.87 mg) was
dissolved in freshly prepared buffer pH 8.0 (5 mL). Papain solution 3.889 U/ml: the enzyme (2.1 U/mg, 9.52 mg) was
dissolved in freshly prepared buffer pH 6.2 (5 mL). Lipase solution 2.003 U/ml: the enzyme (3.1 U/mg, 3.23 mg) was
dissolved in freshly prepared buffer pH 8.0 (5 mL). DTNB solution 3 mM: DTNB (23.8 mg) was dissolved in freshly
prepared buffer pH 8.0 (20 mL) containing NaCl (116.8 mg) and MgCl2 (38.0 mg). ATChI solution 15 mM: ATChI
(43.4 mg) was dissolved in bi-distilled water (10 mL). BTChI solution 15 mM: BTChI (47.6 mg) was dissolved in bi-
distilled water (10 mL). 4-NA solution 6 mM: 4-NA (21.6 mg) was dissolved in methanol (2.2 mg) and bi-distilled
water (17.8 mL). All solutions were stored in Eppendorf caps in the refrigerator or freezer, if necessary. The pure
compounds were initially dissolved in DMSO, galantamine hydrobromide as standard for AChE and BChE was
dissolved in bi-distilled water. The final concentrations for the enzymatic assay were yielded by diluting the stock
solution with bi-distilled water. No inhibition was detected by residual DMSO (<0.5 %).
4.2.3.3. Enzyme Assay
Cholinesterase assay. A mixture of the DTNB solution (125 µL), enzyme (25 µL) and compounds solutions (25 µL, 3
different concentrations and once water) was prepared and incubated at 30 °C for 20 min. The substrate (25 µL, 4
different concentrations) was added to start the enzymatic reaction. The absorbance data (l = 415 nm) was recorded
under a controlled temperature of 30 °C for 30 min at 1 min intervals. All measurements were performed as triplicates.
The used substrate concentrations in the test were as follows: [ATChI] = [BTChI] = 0.9375 mM, 0.625 mM, 0.325 mM,
0.1875 mM. The mode of inhibition as well as Ki and Ki′ were determined using Lineweaver-Burk plot[42], Dixon
plot[43] and Cornish-Bowden plot[44].
bCA II-assay and lipase-assay. A mixture of buffer solution pH 8.0 (125 µL), enzyme (25 µL) and compounds solutions
(25 µL, 50 µM) was prepared and incubated at 37 °C for 20 min. 4-NA (25 µL, 0.75 µM) was added to start the
enzymatic reaction. The absorbance data (l = 415 nm) was recorded under a controlled temperature of 37 °C for 10 min
15

at 1 min intervals. All measurements were performed in duplicate. The relative inhibition was determined as the
quotient of the slopes (compound divided by blank) of the linear ranges.
Papain-assay. The assay was performed like the bCA II and Lipase-Assay using a buffer solution of pH 6.2 instead.
4.2.4. Docking Studies
The 3D structure coordinates of BChE were obtained from the Protein Data Bank, PDB code 1P0I with a 2.00 Å
resolution, and for AChE the PDB code 4BDT with 3.10 Å resolution was used. To prepare the enzymes for the docking
studies, the co-crystallized inhibitor as well as crystallographic water molecules included in the PDB files were
removed. Hydrogen atoms were added and the protonation states were correctly assigned using the Protonate-3D tool
within the Molecular Operating Environment (MOE) 2011.10 software package45, and energy was minimized using
MMFF94x force field. Molecular docking studies were then performed using the GoldScore scoring function from
GOLD 5.1 software package, and each ligand was subjected to 500 docking runs, using Trp82 and Trp86 N atom as
active site center coordinate for 1P0I and 4BDT, respectively. Docking radius was considered 15 Å from the active site
center. Docking protocol was validated by the docking of the co-crystallized inhibitors for each enzyme, respectively,
and RMSD values between docked and crystallographic poses were below 1.5 Å.
Acknowledgements
The authors wish to thank Dr. Ralph Kluge for ESI-MS and Dr. Dieter Ströhl for the NMR measurements. The IR and
UV-vis spectra as well as the optical rotations were measured by Mrs. Jana Wiese. Many thanks are due to Dr. Thomas
Müller from the Dept. of Haemotology/Oncology for providing the cells, and to the “Gründerwerkstatt –
Biowissenschaften” for support. Furthermore, we thank the Fundação para Ciência e Tecnologia (FCT) for the Postdoc
research grant SFRH/BPD/64265/2009 and for the research unit funding Pest-OE/SAL/UI4013/2011.
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39.
GOLD,
version
5.1;
Cambridge
Crystallographic
Data
Centre:
Cambridge,
U.K.;
www.ccdc.cam.ac.uk/products/gold_suite.
40. Chiou, S. Y.; Huang, C. F.; Hwang, M. T.; Lin, G. Comparison of active sites of butyrylcholinesterase and
acetylcholinesterase based on inhibition by geometric isomers of benzene-di-N-substituted carbamates. J. Biochem.
Mol. Toxicol. 2009, 5, 303.
41. P. Skehan, R. Storeng, D. Scudiero, A. Monks, J. McMahon, D. Vistica, J.T. Warren, H. Bokesch, S. Kenney, M.R.
Boyd, New colorimetric cytotoxicity assay for anticancer-drug screening. J. Natl. Cancer Inst. 1990, 82, 1107.
42. Lineweaver, H.; Burk, D. The Determination of Enzyme Dissociation Constants. J. Am. Chem. Soc. 1934, 56, 658.
43. Dixon, M. The determination of enzyme inhibitor constants. Biochem. J. 1953, 55, 170.
44. Cornish-Bowden, A. A simple graphical method for determining the inhibition constants of mixed, uncompetitive
and non-competitive inhibitors. Biochem. J. 1974, 137, 143.
45. MOE, Molecular Operating Environment; Chemical Computing Group: Montreal, Canada, 2012;
18

www.chemcomp.com.
19

Table 1. Inhibitory constants for galantamine hydrochloride, GA and compounds 1-38 (Ki in µM), determined using
Ellman’s assays, employing acetylcholinesterase and butyrylcholinesterase with galantamine hydrochloride and GA as
standards; four different substrate concentrations and four different inhibitor concentrations were used. Each experiment
was performed in triplicate. F is the quotient of [Ki (AChE) / Ki (BChE)]; n.sol. - not soluble.
compound
Ki (AChE)
Ki (BChE)
F
compound
GA
Ki (AChE)
Ki (BChE)
F
galantamine
hydrobromide
0.54 0.01
9.37 0.67
0.06
> 100
> 100
1
2
> 100
19.79 1.13
23.98 0.81
20.76 1.54
n.sol.
> 100
> 100
> 100
> 100
n.sol.
> 100
n.sol.
n.sol.
n.sol.
> 100
> 100
> 2
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
19.98 3.16
18.94 1.09
16.05 3.35
n.sol.
> 100
> 100
> 100
n.sol.
< 0.20
< 0.19
< 0.16
< 0.20
< 0.24
< 0.21
3
4
5
16.23 0.16
28.08 4.43
n.sol.
> 100
> 100
n.sol.
< 0.16
< 0.28
6
17.67 0.34
n.sol.
< 0.18
7
8
n.sol.
23.83 5.74
14.87 3.31
29.63 1.77
13.02 3.51
> 100
> 100
> 100
> 40
< 0.24
< 0.15
< 0.74
< 0.13
9
n.sol.
10
11
12
13
14
16
18
19
20
23.51 8.45
20.69 0.78
> 2
< 0.24
< 0.21
> 100
> 100
5.43 0.91
> 10
13.74 4.60
20.39 5.24
11.73 1.79
40.58 12.78
18.72 2.34
n.sol.
> 100
> 100
> 100
> 100
> 100
n.sol.
< 0.14
< 0.21
< 0.12
< 0.41
< 0.19
> 100
> 18.42
0.56
> 10
41.76 7.37 74.30 16.96
> 100
> 10
> 20
> 100
> 10
9.81 0.32
> 2.04
20

Table 2. Relative inhibition of the enzymes papain, carbonic anhydrase II (bovine erythrocytes), lipase (candida
antarctica), AChE as well as BChE by 19, 23, 31, 33 and 38; the concentration of each compound was 50 µM, except
for 38, where a concentration of c = 10 µM was used due to its limited solubility.
enzyme
papain
bCA II
lipase
19
23
31
33
38
0 %
0 %
0 %
0 %
0 %
0 %
15 %
51 %
58 %
16 %
0 %
0 %
27 %
32 %
49 %
68 %
38 %
68 %
16 %
45 %
43 %
30 %
51 %
35 %
79 %
AChE
BChE
21

Table 3. IC50 values (in µM) for selected derivatives, determined in photometric SRB assays, using non-malignant
murine embryonic fibroblasts (NiH 3T3). Each experiment was performed in triplicate.
compound
19
23
31
33
38a
IC50 (NiH 3T3)
3.05 0.17
> 30
> 30
> 30
> 30
a experiment was limited due to the solubility
22